The present invention relates to a method for determining a rotational velocity of a transducerless polyphase machine that is operated in a field-oriented manner and to a device for carrying out the method.
German Patent Application 195 31 771.8 describes a method in which an established stator-current model space vector and a stator-current actual space vector are, in each case, multiplied by a conjugate complex complex reference space vector and the imaginary components of these products are compared with each other. A system deviation occurring in the imaginary component of the products formed is a measure for the deviation of the model rotor angular velocity from the actual rotor angular velocity. This system deviation is adjusted to zero using an equalizing controller, so that when the system parameters of the real polyphase machine and of the machine model agree, the model rotor angular velocity is also equal to the actual rotor angular velocity. The real components of these products are compared with each other only in response to small stator frequencies, the detected system deviation in the real component of the products formed being used for readjusting the system parameters of the model stator resistance. In this way, a correct readjustment of the model rotor angular velocity is possible in response to small stator frequencies of the polyphase machine. In response to these small stator frequencies, assuming the stator voltage can be preselected, the currents of the real machine and those of the model machine are in practical terms only a function of the parameter of stator resistance and model stator resistance.
One disadvantage of this conventional method is that in response to torques that are high in the range of the breakdown torque, the torque and thus the active components of the stator current changes only slightly in response to a further increase in the rotor angular frequency, and when the breakdown point is exceeded, the system deviation changes its sign. The consequence of this is that the controlled system gain becomes zero and, beyond the breakdown point, even becomes negative, so that a positive feedback arises out of a negative feedback. Thus, using this conventional method and the device for carrying out this method, the polyphase machine can no longer be prevented from falling out of synchronism.
A further disadvantage of this method is that, assuming a stator frequency of zero with an extremely slow change in the rotational velocity, the model rotor angular velocity can no longer be determined using this conventional method.
In addition, the agreement of the identified rotational velocity with the machine rotational velocity is decisively a function of the quality of the machine model that is used. The parameters that are used in the model must therefore be tracked as a function of the operating and working point in order to correctly reproduce the relationships in the machine. In this context, in particular the rotor and stator resistance must be tracked on the basis of changed winding temperatures. Since there is not supposed to be a temperature measurement of the respective winding, the resistances must be identified on-line. In the aforementioned previous German patent application, a method for determining the stator resistance was already indicated, which is particularly necessary in the case of small stator frequencies. The influence of the stator resistance in the middle and upper frequency range is slight.
An identification of the rotor resistance is not possible in roughly stationary operation, since an incorrectly reproduced rotor resistance cannot be distinguished from a mistakenly identified rotational velocity in the stator current. The temperature of the rotor winding cannot simply be measured using measuring techniques, so that frequently the stator and rotor winding temperatures are equated, which, however, is assured only in the first approach. An incorrect rotor resistance nevertheless leads to an incorrectly identified rotational velocity, so that this can not be tolerated particularly in operation without a rotary transducer.
The present invention provides a method and device for determining a rotational velocity of a transducerless polyphase machine that is operated in a field-oriented manner such that the aforementioned disadvantages no longer occur.
As a result of fact that the detected system deviation in the real portion of the products is referred to for identifying the rotational velocity, in the range of the breakdown torque, which is usually required only in the range of high rotational velocities, the controlled system gain has its largest value in response to a clearly determined sign. In the range of small rotor frequencies, there is, however, a clearly reduced controlled system gain. For this reason, the detected system deviations in the imaginary portion and the real portion of the products formed are, in each case, weighted and totals using a factor, so that from small to very high rotational velocities, the rotational velocity can be correctly identified. Thus a machine""s falling out of synchronism can at all times be prevented.
In an advantageous method according to the present invention, a supplementary value is added to a total system deviation. This supplementary value is determined using a flux magnitude modulation, this value being a function, on the one hand, of the selected amplitude and the frequency of the flux magnitude modulation and, on the other hand, decisively of the rotational velocity deviation between the real polyphase machine and the model machine. The larger the rotational velocity error, the larger the value that is added for the total system deviation.
Using this advantageous method, it is possible to precisely identify this rotational velocity irrespective of the quality of the measuring components used, assuming a stator frequency of zero and in response to an extremely slow change of the rotational velocity of the polyphase machine.
In a further advantageous method according to the present invention, a supplementary value is also formed on the basis of a flux magnitude modulation, the value being used for adjusting the model rotor resistance. Since the value additionally determined by the flux magnitude modulation is not needed for identifying the rotational velocity in the middle and upper frequency range, the supplementary value is used in this frequency range for adjusting the model rotor resistance. In this way, the erroneous identification of the rotational velocity caused by an incorrectly reproduced rotor resistance is eliminated, so that in this frequency range the rotational velocity is always correctly identified.
As a result of the method according to the present invention, for determining a rotational velocity of a transducerless polyphase machine that is operated in a field-oriented manner, the rotational velocity of the polyphase machine can now always be precisely identified, from a stator frequency of zero to very high stator frequencies.
In order to further explain the present invention, reference is made to the drawing, in which is schematically represented an exemplary embodiment of a device for carrying out the method according to the present invention for determining a rotational velocity of a transducerless polyphase machine that is operated in a field-oriented manner.